The invention relates to a circuit and a method for the uninterruptible power supply of electronic modules comprising a capacitive energy store, in particular for use in a computer system.
The undesired interruption of the supply of energy in computer systems, even when it is in the region of a few milliseconds, generally suffices to destroy the functioning of the computer system. In the case of computer systems, it is necessary here, in order to carry out a controlled switch-off process in which a loss of important computer data is avoided, to bridge the failure of the regular supply of energy for the time period required for properly shutting down the computer system with the aid of an uninterruptible power supply. In this bridging time, the computer system can then close open files, e.g. sensitive databases, and save important computer data in nonvolatile read only memories.
Uninterruptible power supplies such as are also used, in particular, in computer systems generally comprise rechargeable batteries as energy stores. However, such rechargeable batteries have a high charging time. Furthermore, the current intensity is limited in the case of rechargeable batteries. In the case of computer systems, in particular for use in automation technology, it is preferred to design the uninterruptible power supply as a plug-in card or as part of the motherboard of the computer. However, rechargeable batteries as energy stores have a high space requirement, such that uninterruptible power supplies having rechargeable batteries can be incorporated in computer systems only with difficulty.
Since, in the case of computer systems, generally only interruptions in the regular supply of energy of a few seconds have to be bridged, because this holding time usually suffices for a controlled switch-off of the computer system, use is increasingly being made of capacitive energy stores with which high current intensities can be obtained for a short time and which are distinguished by a small space requirement. So-called double-layer capacitor, having a high efficiency and a long life time, are appropriate as capacitive energy stores for use in an uninterruptible power supply.
One important requirement made of an uninterruptible power supply having a capacitive energy store, primarily when used in computer systems, is rapid starting, in order, in the case of a collapse of the regular supply of energy, to reliably ensure the controlled shutdown or saving of important computer data. When a capacitive energy store is used, it is generally necessary to adapt the voltage specified by storage elements of the uninterruptible power supply to the supply voltage of the computer. Furthermore, when a capacitive energy store is used, it is necessary to ensure that uniform charging or discharging of the individual elements takes place in order to avoid damage or destruction of the capacitive energy store. Furthermore, the uninterruptible power supply, particularly when it is used in a computer system, has to be designed such that a faulty charging or discharging process and a defective capacitive energy store are reliably ascertained.